This invention relates generally to phase shifters and more particularly to compact 180 degree phase shifters.
As is known in the art, phase shifters have a wide range of applications. For example, one such application is with radio frequency signals where the phase shifter provides a selective phase shift to a signal propagating therethrough. More particularly, as is known in the art, phase shifters are employed in various radio frequency (r.f) applications such as phased array antenna systems. One type of phase shifter, a passive phase shifter 10 is shown in FIG. 1 and includes passive elements which provide a phase lag and a phase lead network and includes a pair of signal paths provided between an input terminal RF IN and an output terminal RF OUT with the upper one of the signal paths being through a high pass filter 14 to provide phase lead or positive phase shift to a signal and the lower one of the signal paths being through a low pass filter 18 to provide phase lag or negative phase shift to a signal. Typically, a pair of switches 12, 16 are used to couple a signal between the input and output terminals through a selected one of said filter networks. Often, a pair of field effect transistors are arranged to provide active switching elements of each one of said switches. Field effect transistors are employed in these applications because they are easily formed as part of monolithic integrated circuits unlike other types of active switching devices such as pin diodes. Further, with this approach, impedance matching networks (not shown) are generally required at the input and output of each FET. This results in a loss in bandwidth, increased insertion loss and increased complexity and size of the phase shifter circuit.
Other types of phase shifters are described in U.S. Pat. Nos. 5,148,062 inventor Marc E. Goldfarb issued Sep. 15, 1992 and U.S. Pat. No. 4,733,203 inventor Yalcin Ayasil issued Mar. 22, 1988 both assigned to the same assignee as the present invention. While such phase shifters operate satisfactory in many applications, it is desirable that the size of such phase shifters be minimized.
In accordance with the present invention, a phase shifter is provided for changing the phase of a signal fed thereto. The phase shifter includes a first inductive reactance element and a first capacitive reactance element having one electrode connected to either the input or the output port. The phase shifter includes a first pair of switching elements. A first switching element thereof switches between a conducting state and a non-conductive state when the control signal changes from a first logic state to a second logic state while a second switching element thereof switches between a non-conducting state and a conductive state when the control signal changes from the first logic state to the second logic state. Also provided is a second pair of switching elements. A first switching element thereof switches between a conducting state and a non-conductive state when the control signal changes from a first logic state to a second logic state while a second switching element thereof switches between a non-conducting state and a conductive state when the control signal changes from the first logic state to the second logic state. The phase shifter includes a second inductive reactance element coupled across the first switching element of the first pair of switching elements and a second capacitive reactance element coupled across the second switching element of the second one of the pair of switching elements. The first inductive and first capacitive reacance elements each have a first terminal thereof connected to one of the input and outputs of the circuit. The first inductive reactance has a second terminal thereof connected to a first node and the first capacitive reactance elements has a second terminal thereof connected to a second node. The first switching element of the first pair of switching elements is coupled between the first node and a reference potential and the second switching element of the second pair of switching elements is coupled between the second node and the reference potential. The second switching element of the first pair of switching elements is coupled between the first node and the other one of the input and output ports. The first switching element of the second pair of switching elements is coupled between the second node and said other one of the input and output ports.
In accordance with the invention, a configurable filter is provided. The filter provides high pass filtering between an input port and an output port during a first logic state of a control signal and low pass filtering between the input port and the output port during the second logic state of the control signal. The filter includes first inductive and first capacitive reactance elements along with second inductive and second capacitive reactance elements. The first inductive reactance element and the second capacitive reactance element are connected to a first node and the first capacitive reactance element and the second inductive reactance element are connected to a first node. A switching network is provided. The switching network includes: a first switching element for coupling the first inductive reactance element between the input port and the output port in response to the first logic state of the control signal and for de-coupling the first inductive reactance element from between the input port and the output port in response to the second logic state of the control signal; a second switching element for coupling the first capacitive reactance element between the input port and the output port in response to the second logic state of the control signal and for de-coupling the first capacitive reactance element from between the input port and the output port in response to the first logic state of the control signal; a third switching element for coupling the second capacitive reactance element between the first node and a reference potential during the second logic state of the control signal and for shunting the second capacitive reactance element to couple the first node to the reference potential during the first logic state of the control signal; and a fourth switching element for coupling the second inductive reactance element between the second node and the reference potential during the first logic state of the control signal and for shunting the second inductive reactance element to couple the second node to the reference potential during the second logic state of the control signal.
With such arrangements, a compact phase shifter is provided adapted to change the phase of a signal fed to the input port of such phase shifter 180 degrees as such signal passes through the phase shifter in response to a logic state change in a binary control signal fed to the circuit.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.